This invention is directed to roll forming machines and, more particularly, to pinch and pyramid roll forming machines.
Tapered structural members are used in a variety of different environments. In many cases, as well as being tapered, structural members must also be contoured. For example, large transport aircraft utilize sheet metal structural members in the form of stringers, longerons and frames. For optimum structural efficiency, the section modulus of these structural members (based on section height and thickness) must vary to suit loading conditions. That is, if the section modulus is highest where the load is greater and lower when the load is less (as opposed to a continuous section modulus based on the maximum loading capacity), maximum weight efficiency is obtained. In this regard, since an airplane body is loaded as a beam, stresses are highest at the crown and keel of the aircraft and diminish toward the forward and aft ends. As a result, in order to obtain maximum structural efficiency, stringers must have substantially greater height in the mid-region of the aircraft and frames must have a substantially greater height in the crown and keel areas. Both frames and stringers, of course, are normally contoured, i.e., curved.
In the past, tapered structural members, regardless of whether or not they were contour formed, were built from small pieces spliced together with associated doublers, fail safe members and fasteners, as necessary. Obviously, there are weight penalties associated with this approach, as well as undesirably high manufacturing costs. Recently, an apparatus for producing elongate, tapered structural members in a continuous manner has been developed. In this regard, attention is directed to U.S. Pat. No. 4,006,617 entitled "Method and Apparatus for Roll Forming Tapered Structural Members". While the method and apparatus described in this patent greatly reduces the weight and manufacturing costs attendant to the production of linear, elongate, tapered structural members, it does not solve the same problems with respect to contoured, tapered structural members.
In the past, structural members of continuous uniform cross-sectional geometry usually have been contour roll formed either by pinch roll forming machines or by pyramid roll forming machines. Each of these types of machines has advantages and disadvantages when compared to the other type. As a result each is more useful in some circumstances than the other.
A pinch roll forming machine comprises two vertically opposed matched pinch rolls and two outrigger or forming rolls, one on either side of the pinch rolls. The pinch rolls are driven and move the structural member as it is being contoured (curved). In addition, during forming, the pinch rolls restrain buckling in the critical forming area. The outrigger or forming rolls impart contour to the structural member or part as these rolls are progressively raised from an original in-line position. One advantage of pinch roll forming machines is the high degree of part confinement provided in the bending area. A further advantage is the high pinch roll pressure that can be utilized to thin part flanges located on the outer periphery of the contour in order to relieve compressive stresses on inner flanges. Pinch roll forming machines have the disadvantage that one more roll assembly is required (when compared to pyramid roll forming machines described below). Also, since more degrees of roll movement are involved, additional control axes mechanisms are required. In addition, heavy roll assemblies are required and, unless the forming rolls are driven, the possibility of part scuffing is high.
Pyramid roll forming machines comprise three driven rolls with two lower, in-line rolls supporting a structural member while it is being contoured (curved) by an upper, transversely adjustable, roll located midway between the two lower rolls, which are mounted for rotation in fixed positions. One advantage of pyramid roll forming machines is that they include fewer roll assemblies than do pinch roll forming machines; and only one roll is position controlled. Also, since all three rolls are driven, the possibility of part slippage and skidding during the part contouring operation is minimized. A disadvantage of pyramid roll forming machines is the lack of a high degree of part confinement in the critical forming area. As a result, such machines are not generally suitable for contouring thin, deep sections. Moreover, generally, pyramid roll forming machines are not as versatile as pinch roll forming machines. For example, they can only contour a part in a single plane, as opposed to contouring a part in two planes, or twisting a part as it is being contoured in one or more planes.
From the foregoing general summary of the nature and operation of pinch and pyramid roll forming machines, as noted above, it will be appreciated each machine has advantages and disadvantages. As a result, the nature of the part to be contour formed and the number to be formed generally dictates the type of machine that will create the desired contour in the required number of parts in the least expensive manner.
One disadvantage of both pinch and pyramid roll forming machines, and the disadvantage to which the present invention is primarily directed, relates to their inability to contour form elongate, tapered structural members. More specifically, in the past, pinch and pyramid roll forming machines were suitable for contouring structural members only if the member or part was of constant cross-section such that the rolls could be machined or assembled from segments to a profile closely matching the part cross-section. This arrangement is necessary to optimize confinement of the part shape particularly in the critical bending area. If this requirement is not met, the higher stressed regions of the member are free to buckle and distort during contouring. Because the rolls are of constant profile, the overall machines lack the flexibility to contour tapered structural members i.e., structural members of varying height.
Therefore, it is an object of this invention to provide a new and improved pinch roll forming machine.
It is another object of this invention to provide a new and improved pyramid roll forming machine.
It is also an object of this invention to provide a pinch roll forming machine suitable for contouring elongate, tapered structural members.
It is a further object of this invention to provide a pyramid roll forming machine suitable for contouring elongate, tapered structural members.
In the past, various proposals have been made to numerically control pinch and pyramid roll forming machines. (Numerical control means the controlling of the mechanically movable elements of such machines by a controller in accordance with numerical instructions stored in a suitable memory source, such as a punch tape, solid state memory, or magnetic cards or tapes and the like.) In this regard, attention is directed to U.S. patent application, Ser. No. 756,359 entitled "Pinch and Roll Forming. Assembly for Numerically Controlled Contour Forming Machines", filed Jan. 3, 1977 by Gene B. Foster, and U.S. Pat. Nos. 3,854,215, 3,906,765 and 3,955,389 for their disclosure of numerically controlled contour roll forming machines; and, U.S. patent application, Ser. No. 756,360, entitled "Numerically Controlled Pyramid Roll Forming Machine", filed Jan. 3, 1977 by Gene B. Foster, for its disclosure of numerically controlled pyramid roll forming machines. While the machines described in these patents and applications are advances in the state of the art of pinch and pyramid roll forming machines, they provide no mechanism for contouring elongate, tapered structural members.
Therefore, it is yet another object of this invention to provide an improved numerically controlled pinch roll forming machine suitable for contouring elongate, tapered structural members.
It is a still further object of this invention to provide an improvement numerically controlled pyramid roll forming machine suitable for contouring elongate, tapered structural members.